This program of research is designed to evaluate certain factors related to the use of the cochlear implant for the treatment of deafness. The major objective is to provide systematic psychoacoustic information on hearing capacity that is provided by the cochlear prosthesis. Measures of neurophysiological events evoked by prosthesis stimulation will be evaluated. Our objective will be to provide information on the neurophysiological mechanisms that underlie auditory behavior associated with the cochlear implant. Side effects of implantation and stimulation of the cochlea on vestibular function will be evaluated with a standard battery of human electrostagmographic tests and resulting histological changes will be evaluated. This work will be done in the monkey.